RMS Delay Spread Research Articles

Time dispersion analysis and capacity for ultra wideband channel in indoor environment

In this paper, the ultra wideband (UWB) channel characterisation based on time dispersion analysis is presented. The UWB channel behaviour is different from narrowband and wideband channels due to the large bandwidth, which is the major concern for the channel capacity. In addition, the large bandwidth leads to increased channel variation. The channel characteristics and analysis are important to track the behaviour of UWB channel. The channel measurements were conducted in an indoor environment for UWB system in line-of-sight (LOS) scenario. Time dispersion parameters, namely, root mean squared (RMS) delay spread and mean excess (MN.EX) delay, are analysed based on these measurements. The effectiveness of multipath components is also investigated by means of the multipath gain (MG) and channel capacity. The presented results show that there is a correlation between RMS delay spread and transmitter-receiver (TX-RX) separation distance. The results also show that the best fitting for the RMS delay spread is the Weibull model and the maximum MG is 4.1 dB, which is calculated at the maximum TX-RX separation distance. The channel capacity of multipath components outperforms the capacity of the LOS path by 0.3 bps/Hz.

Time dispersion analysis and capacity for ultra wideband channel in indoor environment

In this paper, the ultra wideband (UWB) channel characterisation based on time dispersion analysis is presented. The UWB channel behaviour is different from narrowband and wideband channels due to the large bandwidth, which is the major concern for the channel capacity. In addition, the large bandwidth leads to increased channel variation. The channel characteristics and analysis are important to track the behaviour of UWB channel. The channel measurements were conducted in an indoor environment for UWB system in line-of-sight (LOS) scenario. Time dispersion parameters, namely, root mean squared (RMS) delay spread and mean excess (MN.EX) delay, are analysed based on these measurements. The effectiveness of multipath components is also investigated by means of the multipath gain (MG) and channel capacity. The presented results show that there is a correlation between RMS delay spread and transmitter-receiver (TX-RX) separation distance. The results also show that the best fitting for the RMS delay spread is the Weibull model and the maximum MG is 4.1 dB, which is calculated at the maximum TX-RX separation distance. The channel capacity of multipath components outperforms the capacity of the LOS path by 0.3 bps/Hz.

Investigation of MIMO Channel Characteristics in a Two-Section Tunnel at 1.4725 GHz

This paper presents results from a wide band single-input–single-output (SISO) and 16 × 16 virtual multiple-input–multiple-output (MIMO) measurement campaign at a center frequency of 1.4725 GHz in a 100-meter long tunnel laboratory which is terminated by a vertical wall with a metallic door. The path loss, root-mean-square delay spread (RMS-DS) characteristics, and power delay profiles (PDPs) are described. In addition, we provide results for the MIMO channel amplitude matrix, which offers a new perspective in understanding MIMO characteristics in tunnel scenarios. Our measurement results are analyzed and compared to ray tracing simulations. The relationships among the angle spread, channel matrix singular values, and MIMO capacity at various link distances are illustrated, and these provide insights into MIMO system deployment.

Impacts of Absorber Loadings on Simulating the Multipath Channel in a Reverberation Chamber

In reverberation chambers, the multipath channels with different delay characteristics can be generated by loading the chamber with different amounts of absorbers. This paper investigates the impacts of absorber loadings on the delay characteristics based on realistic measurements. An efficient method for estimating the root-mean-square (rms) delay spread in the chamber is presented. Furthermore, it is found that the chamber loadings also significantly affect the quality of a digitally modulated signal and the corresponding modulation quality measurements are performed.

A Statistical Channel Model for 2.4GHz Radio Propagation in Ruins Environment

It is of great significance in emergency rescue for earthquake disasters to locate the trapped people using mobile phone Wi-Fi. However, the positioning precision depends on the accuracy of the radio propagation channel model of the ruins environment. In this work, we investigate the channel model in 2.4GHz by measurement in the ruins of Beichuan City, and obtain the parameters of large scale path loss model and delay spread. It is worthy to note that the signal attenuation through ruins is the sum of attenuation through different layered barriers, and the attenuation factors of ferroconcrete and cement brick are 0.72dB/cm and 0.43dB/cm separately. The accuracy of the proposed penetration loss model through ruins is evaluated by the measured data. Moreover, the distribution of RMS delay spread is analyzed according to the cumulative distribution function (CDF) of measured data and evaluated by Kolmogorov-Smirnov (K-S) and Chi-square goodness-of-fit test. The approximation of a linear dependency between mean delay spread and RMS delay spread is also confirmed. This work provides valuable results for the design of mobile Wi-Fi position system in ruins environment.

Experimental Characterization of Multipath Channels for Ultra-Wideband Systems in Indoor Environment Based on Time Dispersion Parameters

In this paper, the multipath effects for UWB channel is presented. The time dispersion parameters; mainly root mean square (RMS) delay spread and mean excess delay are used to characterize the multipath UWB channel. The multipath power; namely multipath gain (MG) parameter is used to characterize the multipath components for line of sight (LOS) and non-line of sight (NLOS) scenarios. All these parameters are extracted from UWB channel measurements in indoor environments. Furthermore, the variation of UWB channel in NLOS scenario is studied within very small movement. Two types of antennas, omnidirectional and directional antennas are used to investigate the multipath effects in UWB channel. The results show that the correlation between RMS delay spread and MG is low for LOS and NLOS scenarios. For very small movement NLOS scenario, the findings are reported that the multipath channels change slowly till 8 cm, however, they have significant changes for 20 cm. It shows that the correlation between investigated parameter is high.

Feasibility study and spatial–temporal characteristics analysis for 28 GHz outdoor wireless channel modelling

This study presents analyses of the feasibility for the 28 GHz band with a comprehensive overview of important channel parameters. A channel measurement system with a time synchronisation scheme is also introduced which is a sliding correlator channel sounder using 250 Mcps (Mega-chips-per-second) pseudo-random noise sequences. The system enables the observation of the behaviour of 28 GHz wave propagation not only to use of forming narrow beams in certain directions (classical narrow beam beamforming) but also omni-likely. This novel synchronised system makes it possible to analyse the wideband channel characteristics. The outdoor channel measurements are conducted considering various features such as foliage effects, signal outage, path loss and outdoor-to-indoor conditions. Furthermore, the spatial channel modelling for omni-like observations with temporal characteristics is firstly interpreted through analysing the essential channel modelling parameters, including the number of clusters, excess delay, root-mean-square (RMS) delay spread, power delay spectrum, and angular spread. In the authors’ measurements, the average number of clusters was 2.41 with standard deviation of 1.44. The average RMS delay spread was 36.06 ns with standard deviation of 46.73 ns. Furthermore, the mean values of the RMS azimuth spreads of the angle of departure and arrival were 6.65° and 24.04°, respectively.

Statistical Modelling and Characterization of Experimental mm-Wave Indoor Channels for Future 5G Wireless Communication Networks.

This paper presents an experimental characterization of millimeter-wave (mm-wave) channels in the 6.5 GHz, 10.5 GHz, 15 GHz, 19 GHz, 28 GHz and 38 GHz frequency bands in an indoor corridor environment. More than 4,000 power delay profiles were measured across the bands using an omnidirectional transmitter antenna and a highly directional horn receiver antenna for both co- and cross-polarized antenna configurations. This paper develops a new path-loss model to account for the frequency attenuation with distance, which we term the frequency attenuation (FA) path-loss model and introduce a frequency-dependent attenuation factor. The large-scale path loss was characterized based on both new and well-known path-loss models. A general and less complex method is also proposed to estimate the cross-polarization discrimination (XPD) factor of close-in reference distance with the XPD (CIX) and ABG with the XPD (ABGX) path-loss models to avoid the computational complexity of minimum mean square error (MMSE) approach. Moreover, small-scale parameters such as root mean square (RMS) delay spread, mean excess (MN-EX) delay, dispersion factors and maximum excess (MAX-EX) delay parameters were used to characterize the multipath channel dispersion. Multiple statistical distributions for RMS delay spread were also investigated. The results show that our proposed models are simpler and more physically-based than other well-known models. The path-loss exponents for all studied models are smaller than that of the free-space model by values in the range of 0.1 to 1.4 for all measured frequencies. The RMS delay spread values varied between 0.2 ns and 13.8 ns, and the dispersion factor values were less than 1 for all measured frequencies. The exponential and Weibull probability distribution models best fit the RMS delay spread empirical distribution for all of the measured frequencies in all scenarios.

Large-scale path loss models and time dispersion in an outdoor line-of-sight environment for 5G wireless communications

This paper presents path loss models and time dispersion parameters for different candidate frequencies above 6GHz for fifth-generation (5G) wireless communications. Three well-known path loss models are compared for single-frequency and multi-frequency schemes: the close-in (CI) free space reference distance model, the floating intercept model (FI), and the alpha-beta-gamma (ABG) model. This paper also proposes a new path loss model to account for frequency attenuation (FA) with distance, which we term the FA path loss model. In this model, we introduce a frequency-dependent attenuation factor XF(f), which directly adds to the CI reference attenuation. Ultra-wideband measurements are conducted for different frequencies in the range of 10–40GHz in an outdoor environment for line-of-sight scenarios. The time dispersion parameters mean excess delay, root mean square delay spread (RMS-DS), and maximum excess delay are estimated. The results reveal that the path loss exponent values for CI models are less than 1.4 in our experimental set-up. For the proposed FA model, with a path loss exponent of 1.4, the XF(f) attenuation factor values are less than 9.7dB. The time dispersion findings from this work reveal that the RMS-DS values varied between 0.1 and 1.7ns.

Broadband Characteristics for Multi-Path Power Line Communication Channels: Indoor Environments

In this paper we propose a broadband frequency-domain model for practical indoor power-line communication (PLC) channels. We consider a top-down strategy where the channel is regarded as a multipath propagation environment with frequency-selective fading. The model is based on the physical signal propagation effects of numerous PLC architectures which comprise unknown number of branches and load conditions. We further consider the attenuation of a typical power-line to be increasing with length as well as frequency. The applicability of the model is verified with measurements from real channels from our laboratories and offices within the band 1-30 MHz. The generated channel frequency response (CFR) has a good agreement with measurements results from real PLC channels. Furthermore, to improve the generality of the model application, we study the dispersive nature of these channels through their impulse responses (IR), and then compare our results with findings from elsewhere. The comparison is made in terms of the maximum excess delay, mean excess delay and root mean square (rms) delay spread.

Effects of urban microcellular environments on ray-tracing-based coverage predictions.

The ray-tracing (RT) algorithm, which is based on geometrical optics and the uniform theory of diffraction, has become a typical deterministic approach of studying wave-propagation characteristics. Under urban microcellular environments, the RT method highly depends on detailed environmental information. The aim of this paper is to provide help in selecting the appropriate level of accuracy required in building databases to achieve good tradeoffs between database costs and prediction accuracy. After familiarization with the operating procedures of the RT-based prediction model, this study focuses on the effect of errors in environmental information on prediction results. The environmental information consists of two parts, namely, geometric and electrical parameters. The geometric information can be obtained from a digital map of a city. To study the effects of inaccuracies in geometry information (building layout) on RT-based coverage prediction, two different artificial erroneous maps are generated based on the original digital map, and systematic analysis is performed by comparing the predictions with the erroneous maps and measurements or the predictions with the original digital map. To make the conclusion more persuasive, the influence of random errors on RMS delay spread results is investigated. Furthermore, given the electrical parameters' effect on the accuracy of the predicted results of the RT model, the dielectric constant and conductivity of building materials are set with different values. The path loss and RMS delay spread under the same circumstances are simulated by the RT prediction model.

Use of a Cavity Loaded With a Conductive Liquid to Simulate In-Vehicle Wireless Multipath Channels

In this paper, we describe how we can finely adjust the electromagnetic losses inside a mode-stirred reverberation chamber (MSRC) using a device containing a variable quantity of conductive liquid. This device can be used for several applications such as decreasing the lowest usable frequency in MSRCs for electromagnetic compatibility (EMC) tests or controlling the root-mean-square (rms) delay spread inside a configured MSRC to reproduce the wireless multipath channel of different electromagnetic (EM) environments such as those inside vehicles. In this study, we will focus on wireless environment simulation applications. The rms delay spread is determined inside a cavity provided with apertures and a stirrer and loaded with a conductive liquid. It is compared to that obtained inside an automotive vehicle for different positions of a couple of wireless communication antennas. The comparisons show that, in our case, the static wireless multipath channel of a complex EM environment of a vehicle may be simulated inside such a cavity.

Sensitivity analysis of ray tracing to the geometrical description of the environment

In ray-tracing-based propagation modelling, the electromagnetic field at the receiver is obtained by coherent summation of the fields of multipath components. It is therefore crucial to accurately calculate the phase of the electromagnetic field of each ray. In practice, when preparing the plan of the environment for ray tracing simulation, the lateral positions of the walls may not be included accurately in the database. This alters the phases of the fields as well as the delays of arrival of multipath components which may consequently lead to less accurate results. In this study, the sensitivity of ray tracing results to this type of geometrical inaccuracy is investigated through the propagation of uncertainty approach. The lateral wall positions are assumed random variables and the statistical moments of the received power and rms delay spread are analytically derived and confirmed. A reliability measure is then defined to explore the impact of the geometrical inaccuracy on the ray tracing results. Numerical results are presented for a typical indoor environment at 2.44 GHz. It is observed that the rms delay spread has negligible sensitivity to lateral wall position uncertainty whereas the received power shows more sensitivity with errors of the order of a few dB.

Empirical Models of the Azimuthal Reception Angle—Part II: Adaptation of the Empirical Models in Analytical and Simulation Studies

This paper focuses on modeling of the statistical reception angle properties that are the result of the environmental influence on transmitted signals. Numerous measurements have shown that the statistical properties of angle of arrival (AOA) significantly depend on the type of propagation environment. In practice, this means that in the analytical and simulation studies, the use of statistical models of AOA required their adaptation to propagation conditions in research scenario. Despite the large number of papers that are devoted to the AOA modeling, the method of fitting models to the environment is not presented in any of the publications. This paper fills this gap. For the assessment of the propagation properties and environment type classification, the basis is the rms delay spread (DS). Therefore, the presented method of the model adaptation to the environment type consists of determining the relationship between the model parameter and DS of environment. Here, the probability density function (PDF) of models such as the modified Gaussian, modified Laplacian, modified logistic, and von Mises distribution are considered as the statistical models of azimuth AOA. For seven different propagation environments, the measurement results are used as a reference data. A comparative analysis shows that the modified Laplacian PDF provides the smallest error fit to measurement data. However, in theoretical analysis and simulation studies, other empirical models can be used due to relatively low approximation errors. The presented results are the basis for the adaptation error assessment of the empirical model for any of the research scenario.

Comparison of Three Non-Imaging Angle-Diversity Receivers as Input Sensors of Nodes for Indoor Infrared Wireless Sensor Networks: Theory and Simulation.

In general, the use of angle-diversity receivers makes it possible to reduce the impact of ambient light noise, path loss and multipath distortion, in part by exploiting the fact that they often receive the desired signal from different directions. Angle-diversity detection can be performed using a composite receiver with multiple detector elements looking in different directions. These are called non-imaging angle-diversity receivers. In this paper, a comparison of three non-imaging angle-diversity receivers as input sensors of nodes for an indoor infrared (IR) wireless sensor network is presented. The receivers considered are the conventional angle-diversity receiver (CDR), the sectored angle-diversity receiver (SDR), and the self-orienting receiver (SOR), which have been proposed or studied by research groups in Spain. To this end, the effective signal-collection area of the three receivers is modelled and a Monte-Carlo-based ray-tracing algorithm is implemented which allows us to investigate the effect on the signal to noise ratio and main IR channel parameters, such as path loss and rms delay spread, of using the three receivers in conjunction with different combination techniques in IR links operating at low bit rates. Based on the results of the simulations, we show that the use of a conventional angle-diversity receiver in conjunction with the equal-gain combining technique provides the solution with the best signal to noise ratio, the lowest computational capacity and the lowest transmitted power requirements, which comprise the main limitations for sensor nodes in an indoor infrared wireless sensor network.

Analysis of MIMO Capacity Dependence on Multi-Antenna Channel Delay Spread in Reverberation Chamber

Reverberation chambers are cost-effective tools for evaluating Multiple-Input Multiple-Output (MIMO) Over-The-Air (OTA) communication devices performance in both indoor and outdoor urban channel models. Their performance is typically assessed by using several figures-of-merit (FOM), such as MIMO Capacity, which evaluates the amount of information that can be reliably transmitted over a communications channel. Nevertheless, scarce publications about the effect of the environment characteristics, such as delay spread, on this figure-of-merit can be found in the literature. In this contribution, we analyze the dependence of MIMO Capacity on channel delay spread, by means of a multi-antenna OTA communication system using a QPSK modulation. For that purpose, channel RMS delay spread has been varied inside the reverberation chamber loading it with different quantities of absorbing material.

UWB CHANNEL CHARACTERIZATION IN 28 GHZ MILLIMETER WAVEBAND FOR 5G CELLULAR NETWORKS

The demands of high data rate transmission for future wireless communication technologies are increasing rapidly. The current bands for cellular network will not be able to satisfy these requirements. The millimeter wave (mm-wave) bands are the candidate bands for the future cellular networks. The 28 GHz band is the strongest candidate for 5G cellular networks. The large bandwidth at this band is one of the main parameters that make the mm-wave bands promising candidate for the future cellular networks. To know the wideband channel behavior in mm-wave bands, the wideband channel characterizations are required. In this paper, the 3D WINNER model is used to model the wideband channel at 28 GHz band. Based on this model, the time dispersion parameters at 28 GHz mm-wave band are investigated. The root mean square delay spread and the mean excess delay are the main parameters that can be used to characterize the wideband channel. Morever, the cumulative distribution function (CDF) is used to model the RMS delay spreads. The results show that the RMS delay spread varies between 4.1 ns and 443.7 ns.

Sensitivity of power and RMS delay spread predictions of a 3D indoor ray tracing model.

This study investigates the sensitivity of a three-dimensional (3D) indoor ray tracing (RT) model for the use of the uniform theory of diffraction and geometrical optics in radio channel characterizations of indoor environments. Under complex indoor environments, RT-based predictions require detailed and accurate databases of indoor object layouts and the electrical characteristics of such environments. The aim of this study is to assist in selecting the appropriate level of accuracy required in indoor databases to achieve good trade-offs between database costs and prediction accuracy. This study focuses on the effects of errors in indoor environments on prediction results. In studying the effects of inaccuracies in geometry information (indoor object layout) on power coverage prediction, two types of artificial erroneous indoor maps are used. Moreover, a systematic analysis is performed by comparing the predictions with erroneous indoor maps and those with the original indoor map. Subsequently, the influence of random errors on RMS delay spread results is investigated. Given the effect of electrical parameters on the accuracy of the predicted results of the 3D RT model, the relative permittivity and conductivity of different fractions of an indoor environment are set with different values. Five types of computer simulations are considered, and for each type, the received power and RMS delay spread under the same circumstances are simulated with the RT model.

The Evaluation of Probe Signals for Impulse Response Measurements in Shallow Water Environment

Understanding the characteristics of channel propagation plays an important role in designing communication systems. Underwater acoustic channel modeling is commonly done by the direct measurement result from a specific location and time. This paper presents an evaluation of channel impulse response (CIR) and power delay profile (PDP) measurements in shallow water environment using three types of probe signals, i.e., pseudonoise (PN)-sequence, exponentially sine swept (ESS), and amplitude-modulated ESS (AM-ESS). The measurements have been carried out in a laboratory-scale towing tank. The ESS signal has been found to produce CIR and PDP that are close to those of the ray tracing model. The multipath pattern of CIR obtained from ESS signal shows an 80% similarity; it was closer to the ray tracing model compared with other results, made using PN-sequence and AM-ESS signals. The estimated value of rms delay spread obtained by the ray tracing model is 1.023 ms and that obtained by the ESS signal is 1.502 ms. Meanwhile, the values obtained by the PN-sequence and AM-ESS signals are 0.769 and 1.410 ms, respectively. In the frequency domain, the spaced-frequency correlation function, obtained using the PN-sequence and ESS signals, is more similar to the ray tracing model compared with the AM-ESS signal.

Experimental measurement and statistical analysis of the RMS delay spread in time-varying ultra-wideband communication channel

The statistical analysis of the RMS delay spread is achieved based on the results obtained from an outdoor time-varying ultra-wideband (UWB) channel measurement. The paper reports on the RMS delay spread values, the cumulative distribution functions (CDFs) and the probability density functions (PDFs) for the measured channel configurations with their estimated parameters. Findings show how the RMS delay spread values are fluctuating for different channel configurations within the same measurement campaign. For example, 35ns and 2.5ns have been obtained for different channels. The differences in the measured instantaneous RMS delay spread leads to obtaining different PDFs that fit the measured data where Generalized Pareto distribution is dominant. The relation between the RMS delay spread and the channel path loss has been studied. Positive correlation is seen for all measured channels with different amounts. The highest correlation value is 0.7675 while the lowest is 0.2951. The coherence bandwidth analysis is also conducted, and the values are fluctuating as the case of the RMS delay spread. The obtained values varies between 325.3MHz and 5.7MHz.